Human growth hormone (hGH) is multifaceted from a chemical and functional viewpoint. The multiple, seemingly unrelated activities of hGH are difficult to explain by one unifying mechanism of action. Studies on the chemical heterogeneity of circulating hGH as a possible basis for its functional multiplicity have identified several monomeric hGH forms, corresponding oligomers, and hGH fragments in human blood. In the course of these studies, one (or more) circulating binding protein(s) for hGH were discovered. Preliminary data indicate that 50-60% of hGH circulates in complexed form with these biding protein(s). The binding protein is neither albumin nor an immunoglobulin, the mol. wt. of the main binding component is 60-65kD. It is proposed to gain more information about the chemistry, physiology and biological effect of these binding proteins and their complex with hGH by 1) characterizing their physico- chemical properties by high-resolution electrophoretic techniques; 2) purifying sufficient quantities of binding proteins to permit physiological studies; 3) generating antibodies against the binding proteins and developing immunological recognition tools (radioimmunoassay, immunocytochemistry); 4) studying the source and regulation of the binding proteins in health and disease; 5) studying the effect of the binding proteins on the state of hGH in blood and hGH turnover; 6) examining the biological effects of binding proteins and complexed hGH in several systems relevant to GH action. In addition, developed techniques will be used to search for GH-binding proteins in other species. Methods used for characterization of binding proteins include chemical crosslinking with 125hGH, and polyacrylamide gel electrophoresis (PAGE). Binding proteins will be purified by several affinity chromatography steps, gel filtration, PAGE, electrofocusing, ion exchange chromatography and HPLC. Polyclonal and monoclonal antibodies will be raised in rabbits and mice, respectively. Radioimmunoassay and hGH binding assay will be used to measure the blood levels, regulation and tissue source of the binding proteins in health and disease. The effect of the binding proteins on hGH turnover will be studied by a pharmacokinetic rat model. Potential effects of the binding protein on hGH actions will be probed by radioreceptor assay, in vitro bioassay and possibly in vivo bioassay. The studies are relevant to growth disorders, catabolic states, diabetes, and liver disease.